DIAX-T

Indications

• Benign prostatic hyperplasia

Dosage

Adults: 500 micrograms daily, with treatment review at 3–6 months and then every 6–12 months.

Mechanism of action

Dutasteride binds to both type I and type II isoenzymes of 5α-reductase, forming a stable complex that inhibits the conversion of testosterone to DHT. DHT is a key hormone in prostate development and growth, and by reducing its levels by more than 90%, dutasteride alleviates symptoms of BPH and improves urinary flow.

Pharmacodynamics

Dutasteride exhibits a dose-dependent reduction in circulating DHT levels, with maximum effects observed within 1-2 weeks after initial administration. Clinical studies have shown that median serum DHT concentrations were reduced by 85% and 90% after 1 and 2 weeks of daily dosing with 0.5 mg, respectively. Continuous administration of dutasteride maintains DHT levels suppressed in the majority of patients, and it may also lead to decreased serum prostate-specific antigen (PSA) levels in patients with prostate cancer.

Pharmacokinetics

Dutasteride is well absorbed after oral administration, with a peak plasma concentration typically reached within 1-2 hours. The drug has a long half-life, allowing for once-daily dosing. It is extensively metabolized in the liver, primarily by CYP3A4 and CYP3A5 enzymes, leading to the formation of several metabolites. The elimination half-life is approximately 5 weeks, which supports the need for regular follow-up and dose adjustment based on clinical response.

Contra-indications

• History of micturition syncope
• History of postural hypotension

Adverse effects

• Abdominal pain
• Anxiety
• Angioedema
• Arrhythmias
• Asthenia
• Chest pain
• Constipation
• Cough
• Depression
• Dizziness
• Diarrhoea
• Drowsiness
• Fatigue
• Gastrointestinal disturbances
• Hyperhidrosis
• Insomnia
• Myalgia
• Nasal congestion
• Nausea
• Oedema
• Palpitations
• Paraesthesia
• Postural hypotension
• Sexual dysfunction
• Skin reactions
• Syncope
• Vomiting
• Weight gain

Interactions

• Cobicistat increases exposure
• Idelalisib increases exposure
• Clarithromycin increases exposure
• Crizotinib unknown effect on exposure
• Imatinib unknown effect on exposure
• Letermovir unknown effect on exposure
• Nilotinib unknown effect on exposure
• Terazosin may increase risk of hypotension

Precautions

• Caution in elderly patients
• Caution in patients with history of prostate cancer
• Monitor for signs of hypotension and syncope
• Consider lower initial dose in patients with autonomic neuropathy

Pregnancy

Dutasteride is contraindicated in pregnancy due to potential harm to a male fetus.

Breast-feeding

Manufacturer advises avoiding use during breastfeeding due to potential for effects on the infant.

Storage

Store at room temperature, away from moisture and heat.

Formulations

• Dutasteride 0.5 mg capsules

Indications

• Erectile dysfunction (ED)
• Pulmonary arterial hypertension (PAH)
• Benign prostatic hyperplasia (BPH)

Dosage

Children: Not established; refer to the BNF for Children for further guidance.

Adults: Refer to the specific guidelines in the BNF for appropriate dosage.

Mechanism of action

Tadalafil selectively inhibits phosphodiesterase-5 (PDE5), leading to increased levels of cyclic guanosine monophosphate (cGMP). This enhances smooth muscle relaxation in penile tissues during sexual arousal by preventing the breakdown of cGMP, thereby facilitating increased blood flow and erection. In PAH, tadalafil promotes vasodilation of the pulmonary arteries, reducing blood pressure in these vessels. In BPH, it may decrease smooth muscle cell proliferation, alleviating urinary symptoms.

Pharmacodynamics

Tadalafil enhances sexual stimulation-dependent smooth muscle relaxation in the penis, resulting in increased blood flow and erection. In PAH, it produces vasodilation in the pulmonary vasculature, lowering pulmonary artery pressure. For BPH, tadalafil may alleviate urinary symptoms by reducing prostate size and relieving anatomical obstruction. Its lower affinity for PDE6 compared to other PDE5 inhibitors results in fewer visual side effects.

Pharmacokinetics

Tadalafil is well absorbed orally, with peak plasma concentrations occurring within 2 hours. Its bioavailability is approximately 80%, and it has a half-life of approximately 17.5 hours, allowing for once-daily dosing for some indications. Tadalafil is metabolized primarily in the liver via the cytochrome P450 system, mainly CYP3A4, and is excreted as metabolites in the feces and urine. The presence of food does not significantly affect its absorption.

Contra-indications

• Systolic blood pressure less than 90 mmHg
• Concurrent use of nitrates for angina

Adverse effects

• Headache
• Flushing
• Dyspepsia
• Nausea
• Back pain
• Myalgia
• Visual disturbances
• Hearing impairment
• Priapism
• Hypotension

Interactions

• Cobicistat + tadalafil: Moderate (increases exposure)
• Antifungals, azoles + tadalafil: Unknown (increases exposure)
• Crizotinib + tadalafil: Unknown (increases exposure)
• Idelalisib + tadalafil: Unknown (increases exposure)
• Imatinib + tadalafil: Unknown (increases exposure)
• Letermovir + tadalafil: Unknown (increases exposure)
• Nilotinib + tadalafil: Unknown (increases exposure)

Precautions

• Caution in patients with hepatic impairment
• Consider dose adjustment in mild to moderate impairment
• Discontinue if sudden visual impairment occurs

Pregnancy

Use only if potential benefit outweighs risk; no evidence of harm in animal studies.

Breast-feeding

Manufacturer advises avoiding use; no information available.

Storage

Store in a cool, dry place away from light.

Formulations

• Tadalafil 2.5 mg tablets
• Tadalafil 5 mg tablets
• Tadalafil 10 mg tablets
• Tadalafil 20 mg tablets

Mechanism of action

The 5α-reductase is a nuclear-bound steroid intracellular enzyme primarily located in the prostatic stromal cell that converts the androgen testosterone into the more active metabolite, 5α-dihydrotestosterone (DHT). DHT is considered to be the primary androgen playing a role in the initial development and subsequent enlargement of the prostate gland. It serves as the hormonal mediator for the hyperplasia upon accumulation within the prostate gland. DHT displays a higher affinity towards androgen receptors in the prostate gland compared to testosterone and by acting on the androgen receptors, DHT modulates genes that are responsible for cell proliferation. Responsible for the synthesis of approximately one-third of circulating DHT, type I 5α-reductase is predominant in the sebaceous glands of most regions of skin, including the scalp, and liver. The type II 5a-reductase isozyme is primarily found in the prostate, seminal vesicles, epididymides, and hair follicles as well as liver, and is responsible for two-thirds of circulating DHT. Due to its dual inhibition of both isoenzymes of 5α-reductase, dutasteride causes a near-complete suppression of DHT. Compared to a 70% reduction of serum DHT levels caused by [finasteride], a near-complete suppression of serum DHT-more than 90% is seen with dutasteride. By forming a stable complex with both type I and type II 5α-reductase, dutasteride inhibits its enzymatic action of converting testosterone to 5α-dihydrotestosterone (DHT), which is the androgen primarily responsible for the initial development and subsequent enlargement of the prostate gland. It is proposed that DHT is the principal androgen responsible for prostatic growth in later life-normal masculinization of the external genitalia and maturation of the prostate gland during development-thus reducing the serum DHT levels results in reduced prostatic volume and increased epithelial apoptosis. Dutasteride is a competitive and specific inhibitor of both Type I and Type II 5α-reductase isoenzymes and when evaluated under _in vitro_ and _in vivo_ conditions, the dissociation of the drug from the drug-enzyme complex is reported to be extremely slow. Dutasteride does not bind to the human androgen receptor.

Pharmacodynamics

Dutasteride is a synthetic 4-azasteroid compound that selectively inhibits both the type I and type II isoforms of steroid 5α-reductase, an intracellular enzyme that converts testosterone to 5α-dihydrotestosterone (DHT). Dutasteride works by reducing the levels of circulating DHT. It was also shown to reduce the size of the prostate gland, improve urinary flow, and symptoms of benign prostatic hyperplasia alone or in combination with tamsulosin. The effect of the reduction of DHT by dutasteride is dose-dependent, with the maximum effect observed within 1-2 weeks following initial administration. After 1 and 2 weeks of daily dosing with dutasteride 0.5 mg, median serum DHT concentrations were reduced by 85% and 90%, respectively. The serum concentrations of DHT were maintained to be decreased by more than 90% in 85% of patients following 1 years' administration of oral dutasteride 0.5 mg/day. As evident from the clinical studies, dutasteride may also cause decreases in serum PSA in the presence of prostate cancer.

Mechanism of action

Tadalafil is a selective phosphodiesterase-5 (PDE5) inhibitor that produces several downstream effects with the most common therapeutic effect being smooth muscle relaxation. Patients may experience ED due to a variety of causes including psychogenic, neurogenic, vasculogenic, iatrogenic, or endocrine. These causes result in dysfunction of penile smooth muscle relaxation through either disrupted neuronal signaling or direct influence on smooth muscle cells. During sexual arousal, non-adrenergic non-cholinergic (NANC) neurons release nitric oxide (NO). Nitric oxide stimulates guanylate cyclase which converts guanosine triphosphate to cyclic guanosine monophosphate (cGMP). cGMP activates the cGMP-dependent kinase (PKG) in a signal cascade which activates K+ channels leading to inhibition of Ca2+ channels, inhibits platelet activation, and inhibits smooth muscle cell proliferation while inducing apoptosis. This signal cascade is attenuated by PDE5 which breaks the phosphodiester bond of cGMP, converting it to GMP. Inhibition of PDE5 by tadalafil increases signaling via the PKG cascade which supports penile smooth muscle relaxation during sexual arousal by decreasing Ca2+ entry into smooth muscle cells. This smooth muscle relaxation allows blood to fill the corpus cavernosum thereby producing an erection. In PAH, blood pressure in the pulmonary arteries is raised due to a variety of mechanisms stemming from endothelial dysfunction. Decreased production of NO and prostacyclin reduce vasodilatory signaling while overproduction of endothelin-1 and thromboxane increase vasoconstriction. Inflammation, thromboses, and hypoxia later contribute to vascular remodeling which further reduces luminal size. The resultant increase in blood pressure reduces the capacity for gas exchange and increases afterload at the right ventricle, producing symptoms of dyspnea, fatigue, and dizziness as well as leading to right-sided heart failure. Tadalafil exerts its therapeutic effect in PAH through boosting NO-cGMP signaling to contribute to smooth muscle relaxation as with ED. Lastly, tadalafil is used to treat BPH. BPH produces urinary dysfunction through hyperproliferation of the epithelial and smooth muscle layers of the prostate. The increased size of the prostate blocks urine flow through the urethra resulting in higher residual volumes due to incomplete emptying. Tadalafil does not appear to exert its benefit via smooth muscle relaxation of the prostate. It may instead exert its effect through a mix of increased oxygenation and decreased inflammation, which decreases tissue remodeling, and inhibition of cell proliferation through the cGMP cascade. The decreased affinity for PDE6 compared to other PDE5 inhibitors may explain the decreased incidence of visual side effects as PDE6 is present in the eye and contributes to color vision. In vitro studies have shown that the effect of tadalafil is more potent on phosphodiesterase type 5 (PDE5) than on other phosphodiesterases. These studies have shown that tadalafil is >10,000-fold more potent for PDE5 than for PDE1, PDE2, PDE4, and PDE7 enzymes, which are found in the heart, brain, blood vessels, liver, leukocytes, skeletal muscle, and other organs. Tadalafil is >10,000-fold more potent for PDE5 than for PDE3, an enzyme found in the heart and blood vessels. Additionally, tadalafil is 700-fold more potent for PDE5 than for PDE8, PDE9, PDE10 and 14-fold more potent for PDE5 than for PDE11A1, an enzyme found in human skeletal muscle. Tadalafil inhibits human recombinant PDE11A1 activity at concentrations within the therapeutic range. The physiological role and clinical consequence of PDE11 inhibition in humans have not been defined. Studies in vitro have demonstrated that tadalafil is a selective inhibitor of phosphodiesterase type 5 (PDE5). PDE5 is found in corpus cavernosum smooth muscle, vascular and visceral smooth muscle, skeletal muscle, platelets, kidney, lung, cerebellum, and pancreas. Penile ere

Pharmacodynamics

Tadalafil exerts a therapeutic effect in ED by increasing sexual stimulation-dependant smooth muscle relaxation in the penis, allowing the corpus cavernosum to fill with blood to produce an erection. Smooth muscle relaxation in the pulmonary vasculature helps to produce vasodilation in PAH which reduces blood pressure in the pulmonary arteries. In BPH, tadalafil may contribute to decreased smooth muscle cell proliferation which may reduce the size of the prostate and relieve the anatomical obstruction which produces urinary symptoms of BPH. The decreased affinity of tadalafil for PDE6 compared to other PDE5 inhibitors may explain the reduced incidence of visual side effects.